As methods for synthesizing hydrocarbons from a syngas, the Fischer-Tropsch reaction, a methanol synthesis reaction, an oxygen-containing C2 (ethanol, aldehyde, etc.) synthesis reaction and the like are well known. And it is known that the Fischer-Tropsch reaction proceeds with a catalyst containing, as an active metal, an iron group element such as iron, cobalt and nickel, or a platinum group element such as ruthenium and the like; the methanol synthesis reaction proceeds with a copper based catalyst; and the oxygen-containing C2 synthesis reaction proceeds with a rhodium based catalyst (see, for example, Non-Patent Document 1).
Incidentally, in recent years, a diesel fuel of a low sulfur content has been desired from the viewpoint of air environmental conservation, and it may be considered that this trend still more increases hereafter. Moreover, from the viewpoint that crude oil resources are limited or from the standpoint of energy security, it is desired to develop an oil alternative fuel, and it may be considered that this development is strongly desired more and more hereafter. As a technology responding to these desires, there is GTL (gas to liquids) which is a technology for synthesizing liquid fuels such as kerosene and diesel fuel and the like from a natural gas (main component: methane) whose proven reserves are said to be comparable to a crude oil in terms of energy.
The natural gas does not contain a sulfur content; or even if it contains a sulfur content, the sulfur content is hydrogen sulfide (H2S) or the like which is easy for desulfurization, and therefore, the resulting liquid fuel such as kerosene and diesel fuel and the like does not substantially contain a sulfur content and possesses an advantage that it can be utilized as a high-performance diesel fuel having a high cetane number. Thus, this GTL has recently attracted attention more and more.
As a part of the foregoing GTL, a method (hereinafter referred to as “FT method”) for producing hydrocarbons from a syngas by the Fischer-Tropsch reaction (hereinafter referred to as “FT reaction”) has been actively investigated. In this FT method, in order to increase a yield of hydrocarbons, it may be considered that it is effective to use a catalyst having an excellent performance whose hydrocarbon-producing ability, namely, the activity is high, the formation of a gaseous component is small, and the activity is stably exhibited over a long period of time.
Then, various catalysts for the FT reaction have hitherto been proposed. For example, there is proposed a catalyst in which an FT active metal species such as cobalt and iron is supported on a metal oxide support made of, for example, alumina, silica, silica-alumina, titania or the like (see, for example, Patent Document 1, Patent Document 2 and Patent Document 3). Moreover, as a catalyst aiming at a high selectivity to olefins, there are proposed ruthenium based catalyst such as a catalyst in which ruthenium is supported on a manganese oxide support, a catalyst in which a third component is further added to this ruthenium-supported catalyst, and the like (see, for example, Patent Document 4 and Patent Document 5).
Though these conventionally proposed catalysts exhibit correspondingly excellent selectivity to olefins and correspondingly catalytic activity in the FT method using the same, a further enhancement of the catalytic activity is being desired. In general, the higher the activity of the catalyst, the higher the productivity of a desired product per weight of the catalyst is. Thus, the use weight of the catalyst for obtaining a desired product of the same amount may be reduced, and following this, downsizing of a reactor and the like can be achieved, so that reduction of catalyst expenses or equipment expenses can be expected. Moreover, with respect to the catalyst for the FT reaction, it is desirable that the formation of a gaseous component such methane and the like in the product is small, and the yield of useful liquid hydrocarbons such as kerosene and diesel fuel is high.